1. Field of the Invention
The present invention relates to a method for removing a photoresist layer and polymers layer in the fabrication of a semiconductor device. More particularly, the present invention relates to a high-density plasma method using mixing gases as source for removing a photoresist layer and polymers layer generated during plasma etching process.
2. Description of the Related Art
In the fabrication procedure of a metal oxide semiconductor (MOS), photoresist layers are widely used in patterning processes. However, after an etching step is performed, the photoresist layer and the sidewall polymers generated during plasma etching step needs to be removed for subsequent processes. When the photoresist/polymers layer is not removed completely, the residue affects subsequent processes and debases the quality of the device. Accordingly, it is important to avoid leaving any photoresist/polymers layer residue when the photoresist/polymers layer is removed.
In the conventional photolithography method, integrated circuit patterns transferred on wafers comprises steps of coating a photoresist layer over the wafer. The photoresist layer is sensitive to light and resistant to etching. The image of the master mask is replicated on the photoresist layer by an exposure system to form a photoresist layer. An etching step is performed to form the predetermined pattern on the wafer by using the patterned photoresist layer as an etching mask layer. At present, high-density plasma (HDP) is usually used to perform an anisotropic etching step, and during the etching step, heavy sidewall polymers are deposited to meet etching requirements (e.g. etching selectivity to substrate and profile control etc.). Following the oxide plasma etching, the patterned photoresist layer and sidewall polymer layers are stripped away in-situ. However, during high-density plasma etching, some undesirable residues are generated and accumulated on the surface of the photoresist layer and/or the sidewall of the opening formed by etching. The residues cannot be removed easily by oxygen plasma and leave on the wafer to affect the subsequent processes. The main residues include the following:
1. Cross-linking polymer generated by ultraviolet irradiation is generated on the top surface of the photoresist layer; PA1 2. Silicon-containing polymer is generated while performing the etching step; and PA1 3. The polymers on the sidewall of the opening are generated during etching from the gasses such as C.sub.4 H.sub.8, CH.sub.2 F.sub.2, and C.sub.3 H.sub.2 F.sub.6.
The residues often cannot be cleaned by solvents and result in contamination and defects in the following subsequent process. Recently, in order to avoid photoresist residues as mentioned above left on the wafer, a bias is applied to the wafer to enhance the ion bombardment when the oxygen (O.sub.2) plasma is performed to remove the photoresist layer.
FIG. 1A is schematic, cross-sectional view of the conventional HDP oxide etcher for removing a photoresist/polymers layer by plasma. FIGS. 1B through 1C are schematic, cross-sectional views of the conventional plasma method for removing a photoresist layer.
As shown in FIG. 1A, a bias is applied on a wafer 114 to enhance the ion bombardment of plasma for removing a photoresist layer 104 (as shown in FIG. 1B).
As shown in FIG. 1B, after an opening 108 is formed, an in-situ oxygen plasma etching step is used to remove the photoresist layer 104 and polymer layer 106. As the residual polymers 106 are generated on the top surface of the photoresist layer 104, it is difficult to strip away the photoresist layer 104 completely.
As shown in FIG. 1C, since the ion bombardment of the oxygen plasma is enhanced, the substrate 100 and an oxide layer 102 underneath the photoresist layer 104 are attacked by the plasma. Accordingly, it is desirable to develop a new method to solve the problems such as the loss of substrate and oxide and an inability to control the critical dimension of the opening during in-situ oxygen plasma etching step.